1. Field of the Invention
The present invention relates to a runflat tire system which allows a vehicle to run safely at a constant speed through a predetermined distance even when an internal pressure of a tire is lowered.
2. Description of the Related Art
In recent years, a runflat tire system by which, even if the tire goes flat, it is possible to travel for a very long distance for example several hundred kilometers at a relatively high speed of up to about 80 km/hr has been proposed.
FIG. 10 shows a conventional system of this kind. The system comprises a tire “a”, a wheel rim b on which the tire “a” is mounted, and a support ring e mounted on the wheel rim b in a cavity “i” surrounded by the tire “a” and the wheel rim b. When an internal pressure of the tire is reduced, the support ring e contacts against an inner surface of a tread portion d to support a load of the tire. The wheel rim b comprises first and second seats b1 and b2 on which first and second bead portions f1 and f2 of the tire “a” are mounted. A mounting part g for the support ring e is provided between the seats b1 and b2.
In this system, when the internal pressure of the tire “a” is reduced due to puncture or the like, the inner surface d1 of the tread portion d contacts against the support ring e. A load applied to the tire “a” is supported by the support ring e and the wheel rim b. Since the first bead portion f1 and the second bead portion f2 are locked between a rim flange and a hump h, the vehicle can run at such speed that no problem is caused in a runflat manner. This system eliminates a need for exchanging tires on a road shoulder, and allows the vehicle to move to a gas station or a service garage. Thus, it is desired that the runflat tires become widespread in terms of safety at the time of high speed running in addition to convenience and comfort.
As noises generated by a tire, there is a road noise. The road noise is generated if air resonates in the cavity i when a vehicle runs on a rough road, and the road noise causes a roaring sound in a frequency range of about 50 to 400 HZ. The road noise is transmitted into a passenger room and becomes a muffled sound, and this offends a passenger in the vehicle. Like general tires, it is important to reduce the road noise for improving habitability also in the runflat tire system.
As shown in FIGS. 11(A) and 11(B), Japanese Patent Application publication No. 2003-502200 (WO 00/76791 A1) proposes a runflat system in which an annular supporting body r mounted on a rim forms a resonator comprising a large number of cavities u defined by supporting wall portions w3 between an outer peripheral wall w1 and an inner peripheral wall w2, and a side plate w4 closes the resonator. The side plate 4 is provided with tubes v which are in communication with the cavities. In this proposal, vibration characteristics of the resonator is optimized by the tubes v based on the principle of the Helmholtz resonator, thereby suppressing the resonance.
According to the former system has a problem that since the side plate w4 is heavy, the entire weight is increased. Further, this system requires complicated and severe operations such as mounting operation of the tubes v on the side plate w4, mounting operation of the cavities on the sidewall w4, and tuning operation of the vibration characteristics of the resonator, so that it takes a lot of trouble to assemble.